The image size is determined by the aspect ratio and the size of your room (or stage).

If your room is 40' wide and you want a wall to wall screen with a one foot masking you would have 38' left for your scope image. Using the scope aspect ratio of 2.35 to 1 you would then have a picture heigth of 16 1/2' by 38'. You should have a minimum ceiling height of 26' to accomplish that. Your flat image would then be 30' wide and side masking would be needed to properly mask in the sides. If you want to have the same width as scope you would then have a flat image that would be 21' high, now requiring a ceiling with a minimum heigth of 30'.

Once you know the image size that you have available the only other thing you need to know is the distance from the projector to the screen and you can consult lens charts to find out the proper size lenses needed to project the correct image size.

You can put these image sizes under slightly lower ceilings, but I wouldn't recommend it. Actually higher would even be better. I also feel that a 38' screen width is too wide for a 40' room, but it is often done today.

If you are talking about Houlton, you have yet to purchase new screens or lenses so you can do what is right. Leave the screens 4' back. Plan for a screen that fills the room wall to wall for scope. Have a common height and then you will have done film right.

The screen was set on the back wall. Directly to its left (on one of 2) and starting dead below the screen is an exit stairs. By moving it out 4 feet we can extend the width by 3-4' and improve the masking as the screen is currently up almost against the ceiling with no place to install masking above it. It's in Houlton. Do you think a 4 foot move will render the lenses unusable?

Sorry I missed this whole topic, because I've been on vacation for the past month. Mind you, I loved the south of France and Barcelona, and didn't think much about bigscreenbiz. Anyway, I've read all the responses to the question, and everyone's given you great advice. Good luck!